In hydraulic elevators, as also in other elevator systems, it is important to endeavor to maximize the safety of passengers. The elevator car may not drop freely nor may its movement reach uncontrolled acceleration of movement and the uncontrolled deceleration of movement following it. Sudden stops with even comparatively small kinetic energy can cause injury of passengers.
New elevator safety regulations require the monitoring and prevention of unintended starting of elevators. In hydraulic elevators prevention of this unintended starting can be arranged in different ways than in rope elevators because hydraulic elevators do not generally have a counterweight or compensating weight, but instead all the force needed for moving the elevator car is transmitted from the hydraulic powerpack of the elevator, along either a hose or pipe to the lifting cylinder of the elevator.
Known in the art is a hydraulic elevator, which is in an elevator hoistway that is in a building. A hydraulic elevator comprises vertical car guide rails, with which the elevator car is guided to move in the elevator hoistway in an essentially vertical direction. The lifting cylinder can be in a space between the wall of the elevator hoistway and the elevator car, or the lifting cylinder can be disposed in a space directly below the elevator car.
A hydraulic elevator can be a so-called rucksack-type elevator that is rear-lifting, wherein the car guide rails are on the same side as the lifting cylinder behind the rear wall of the car, or a side-lifting elevator, wherein the car guide rails and the lifting cylinder are on a side that is beside the side wall, in which case it is possible to achieve a so-called walk-through car, in which the car doors are on opposite walls of the car. The rear wall of the car refers to the opposite wall in relation to the car door and the side wall refers to a wall of the elevator car that is beside the car door.
The lifting cylinder comprises a cylinder part supported essentially vertically on a fixed structure of the elevator hoistway, and a piston rod moving in relation to the cylinder part, which piston rod is arranged in functional connection with the car for moving the car either fixed directly to the car sling of the car or indirectly via a rope. In an indirect drive hydraulic elevator there is a rope diverting pulley at the end of the piston rod, over which pulley a rope is led, which rope is fixed at one of its ends to a fixed structure in the bottom end of the elevator hoistway and at the other end is fixed to the car sling. For producing hydraulic pressure for driving the lifting cylinder, the hydraulic elevator further comprises a hydraulic powerpack, which is usually disposed in a machine room, which is a room separate to the elevator hoistway beside, or in the proximity of, the bottom end of the elevator hoistway.
Hydraulic elevators are very common. Usually they are modernized in such a way that the elevator is kept as a hydraulically driven one, and the hydraulic powerpack and necessary components are replaced with new corresponding ones. A problem in these prior-art modernization methods of a hydraulic elevator is the high costs and slow installation. If it is desired to retrofit to a hydraulic elevator a function for preventing unintended starting, it can be done by replacing the entire hydraulic powerpack with one that is provided with a function for preventing unintended starting. This is, however, slow and expensive in terms of costs, and causes interruption of the operation of the elevator for a long time and causes considerable inconvenience to users at the installation site.
With this invention the aforementioned problems are eliminated. With the method according to the invention the modernizing of a hydraulic elevator to be according to safety regulations can be done quickly and cost-effectively. According to the method a function preventing unintended starting is added to an old hydraulic system by adding to it an electrically-operating valve that is monitored with control means and that acts on the flow of hydraulic fluid of the lifting cylinder. In this way an old hydraulic elevator can be made to be according to new safety regulations inexpensively and reliably and use of the elevator does not need to be interrupted for a long time.